Method and apparatus for improved extrusion of essentially inviscid jets

ABSTRACT

Low viscosity melts, notably metals and their alloys, are spun for extended periods, with attenuation and with induced velocity profile relaxation by spinning the molten materials at appropriate velocities first into a flowing inert gas and then into a film stabilizing gas. The inert gas zone is provided by a &#39;&#39;&#39;&#39;gas plate&#39;&#39;&#39;&#39; having an orifice aligned essentially coaxially with and beneath the extrusion orifice to provide an inert gas flow between the orifice plate and the gas plate.

United States Patent Otstot et a1.

[54] METHOD AND APPARATUS FOR IMPROVED EXTRUSION 0F ESSENTIALLY INVISCIDJETS Roger S. Otstot, Raleigh; John W. Mottern, Cary, both of NC.

Monsanto Company, St. Louis, Mo.

July 2, 1969 Inventors:

Assignee:

Filed:

Appl. No.:

US. Cl ..425/72, 164/66, 164/82, 425/461 Int. Cl. ..D0ld l/00, 322d 11/00 Field of Search ..164/81, 82, 66, 259, 273; 18/8 QD, 8 QM, 8 SCReferences Cited UNITED STATES PATENTS 2,879,566 3/1959 Pond ..l64/81X2,976,590 3/1961 Pond ..164/82 3,048,467 8/1962 Roberts et al ..18/8 QMUX 3,061,874 11/1962 Lees ..l8/8 QM 3,516,478 6/1970 Dunn et al...164/82 X FOREIGN PATENTS OR APPLICATIONS 6,604,168 10/ l 966Netherlands 164/82 Primary Examiner-R. Spencer Annear Attorney !ames W.Williams, Jr., Russell E. Weinkauf and John D. Upham [5 7] ABSTRACT Lowviscosity melts, notably metals and their alloys, are spun for extendedperiods, with attenuation and with induced velocity profile relaxationby spinning the molten materials at appropriate velocities first into aflowing inert gas and then into a film stabilizing gas. The inert gaszone is provided by a gas plate" having an orifice aligned essentiallycoaxially with and beneath the extrusion orifice to provide an inert gasflow between the orifice plate and the gas plate.

3 Claims, 4 Drawing Figures is 1mm: j

METHOD AND APPARATUS FOR IMPROVED EXTRUSION F ESSENTIALLY INVISCED JETSFIELD OF THE INVENTION This invention relates to improvements in theformation of fibers and filaments by melt extrusion of essentiallyinviscid ets.

More particularly, the invention relates to the formation of fibers andfilaments of materials which are essentially inviscid in the melt byextrusion of the molten essentially inviscid materials into atmosphereswhich stabilize the nascent molten fiber or filament prior to breakupcaused by surface tension pending solidification.

BACKGROUND OF THE lNVENTlON Film stabilization of inviscid jets has beenrecognized recently as a practical means for forming filaments andfibers from materials which exhibit extremely low viscosities in theliquid or molten phase. Thus, where materials such as metals, metalalloys and ceramics exhibit viscosities in the molten phase of less thanabout poises and more commonly only a fraction of a poise, the surfacetension of such a free molten filamentary stream is so great in relationto its viscosity that the stream tends to breakup into small spheres orshot before it can be solidified by cooling or quenching by practicalmeans. It has been discovered that the length of the molten inviscidstream or jet, or the time in which such a jet exists as a continuousstream prior to breakup due to its surface tension when extruded atappropriate velocities can be considerably increased by extruding theinviscid jet into an atmosphere which upon contact with the nascentmolten jet forms a thin film on the surface of the molten jet. Thestabilizing film must, of course, be rapidly formed, be a solid or atleast have a viscosity substantially greater than that of the molten jetand the film should be substantially insoluble in the molten jet underthe conditions so that substantial, and desirably complete, continuityof the film is achieved and maintained. The means for film stabilizinginviscid jets are known and are varied as are the materials which may bestabilized. For example. the molten inviscid jet may be extruded intoatmospheres which readily react with the surface of the molten jet toform a film or. the jet may be extruded into atmospheres which decomposeupon contact with the molten jet to form films. Thus, a molten aluminumjet extruded into air is stabilized by the rapid formation of a film ofaluminum oxide, which film is a solid at the optimum extrusiontemperature and which film is substantially insoluble in the molten jet.Aluminum oxide jets, on the other hand, may be extruded into hydrocarbonatmospheres, such as propane, which upon contact with the hot ceramicjet decompose leaving a stabilizing carbon film on the jet. In a specialcase Alber et al. have noted in US. Pat. No. 3,216,076 that the oxidesof certain metals, such as iron, silver and gold, are soluble in theirrespective metallic melts to the extent that they do not serve to formstabilizing films. Alber et al. suggest, therefore, that filaments canbe formed from such materials by the film stabilized melt spinningtechnique by extruding alloys of such metals with compatible metalswhose oxides are substantially insoluble in the molten jet. Thus, thejet of a ferrous alloy containing a small amount of a metal, such asaluminum, the oxide of which is insoluble in the jet can be effectivelystabilized against surface tension promoted breakup, pendingsolidification by normal or even accelerated heat transfer phenomena.

Beyond the basic film stabilization phenomena, above discussed, therehas been little or no recognition or resolution of the problemsencountered by extrusion of molten essentially inviscid materials atextremely high temperatures to form shaped articles. The requirements ofmaterials at very high temperatures and conditions for forming fibersand filaments from essentially inviscid materials in continuousprocesses are manifold and different to the extent that techniques knownand used in the formation of fibers and filaments from viscous melts ofglasses and synthetic polymers are generally not applicable.

it has been noted, for example, that velocity profiles tend to developacross the essentially inviscid jet or stream as it passes through theextrusion orifice. Upon issue from the orifice such velocity profilesthen tend to relax or approach plug flow causing some change in shape ofthe still molten filamentary stream and, where a thin stabilizing filmforms on the surface of the stream as a fragile cylinder about themolten jet prior to relaxation of the velocity profile, changes in shapeof the stream due to velocity profile relaxation tend to rupture orbreak the film to thereby appreciably or wholly negate its in tendedstabilizing function.

Another problem created by the essentially inviscid nature of the moltenfilamentary stream is that the met cannot be attenuated by drawing as inthe case of viscous glassy and polymeric organic materials. Moreover, ifmeans were discovered to effectively elongate the molten jet, the thinstabilizing film would be required to elongate proportionally, otherwiseit would break thereby nullifying its effectiveness in stabilizing thestream. Yet attenuation is important in processes for spinning inviscidmaterials not only because of enhanced production capabilities but alsobecause of the difficulty of making true fine diameter orifices inmaterials which are substantially inert at high temperatures and whichorifice containing materials must be exceedingly strong at hightemperatures to withstand extrusion pressure. Thus, where an orificehaving a diameter of 20 mils in an orifice plate can be employed in thepreparation of a 4 mil diameter filament, for example, the cost and easeof orifice preparation and orifice life are greatly improved.

A further and notable benefit which would result from stream attenuationlies in the greatly reduced pressure requirements necessary to cause themolten charge to flow through the orifice at a desirable extrusionvelocity. Thus, where 1 mil diameter steel filaments are desired apressure of about 400 p.s.i.g. is required to force the jet through a 1mil diameter orifice at a given desirable velocity. Thus, the forceexerted on the orifice is extremely high when considering that thethickness of the orifice plate would probably be less than 4 mils at theorifice. Where attenuation of the jet can be achieved a 1 mil fiber canbe made from a 4 mil orifice, for example, in which case the pressurerequired to extrude the same mass per unit time as in the case of the 1mil orifice would be substantially decreased.

Still another difficulty encountered in the film stabilization techniquefor producing metal and ceramic fibers involves stream deviation wherethe direction of the nascent molten stream tends to migrate away fromthe extrusion axis. This effect frequently involves undesirable stresseson the essentially inviscid liquidous portion of the stream and rendersthe control of tension and aerodynamic effects on the stream difficult,if not impossible. Deviation of the stream is believed to result fromreaction of the stabilizing atmosphere with the molten jet at or withinthe extrusion orifice.

The use of film stabilization as a technique for stabilization ofessentially inviscid jets requires extrusion into atmospheres whichreact rapidly with the surface of the molten jet. It has been observedthat cylindrically shaped extrusion orifices are frequentlynonful-running. That is, a vena contracta may occur within the orificewhich provides a passageway for the film-forming atmosphere to enter theorifice. Growths, believed to be oxides, other reaction products ordecomposition products of the film-forming atmosphere on the orificeplate, have been observed within the orifice and also as tubelikestalactites which grow from the extrusion orifice.

Growths within the orifice alter the extrusion orifice diameter andfrequently cause the jet to veer from the path of the axis of theorifice. Usually such growths grow to the extent that they completelyblock the orifice. No less troublesome are the tubelike growths whichgrow from the orifice. Tubes, like internal growths, alter the courseand diameter of the stream and, additionally, they alter the velocityprofile of the stream insofar as a tube effectively changes the aspectratio of the orifice. Mere blanketing the orifice with an inert gas hasproved to be ineffective to prevent growths in processes for filmstabilization of inviscid jets.

This invention, therefore, is concerned with melt extrusion apparatuswhich result in improvements in the formation of fibers and filaments ofmaterials having very low melt viscosities.

This invention includes among its objectives apparatus for inducingvelocity profile relaxation in a molten inviscid jet prior to theformation of stabilizing films.

Another object of this invention is the provision of apparatus forattenuating an essentially inviscid molten jet prior to filmstabilization without application of substantial extraneous stressesdownstream of the unstabilized liquidous region of the stream whichextraneous stresses are transmitted to said unstabilized liquidousregion.

A further object of this invention involves the substantial inhibitionof growths within the orifice or at the orifice exit and the consequentreduction of deviation or migration of the molten stream from the pathof the axis of the orifice.

BRIEF SUMMARY OF THE INVENTION The above objects of this invention havebeen accomplished by the continuous extrusion of molten essentiallyinviscid inorganic materials through an orifice as a free stream into azone occupied by a flowing inert, gaseous atmosphere and then into azone occupied by film-forming atmosphere as a continuous moltenfilamentary stream or jet. More particularly, the mo]- ten material isextruded through an orifice directly into flowing inert gas occupying afirst zone immediately below the extrusion orifice which fist zonecommunicates with a second zone containing a film-forming atmosphere.The inert gas zone is connected to a source of inert gas which gascontinuously passes through the first zone and flows out of the firstzone through a second orifice or plate throat" which is essentiallycoaxial with the extrusion orifice and which communicates with the zonecontaining a film-forming atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention believedto be novel are set forth with particularity in the appended claims. Theinvention itself together with further objects and advantages may bebest understood by reference to the following description taken with theaccompanying drawings in which:

FIG. I is a cross-sectional schematical view of a typical assembly forspinning essentially inviscid molten materials;

FIG. 2 is a cross-sectional schematical view of an orifice assembly inaccordance with the teachings of the present invention;

FIG. 2a is a plan view of the orifice assembly of FIG. 2; and

FIG. 3 is an enlarged view of the orifice assembly of FIG. 2.

DETAILED DESCRIPTION FIG. 1 depicts a source of a molten essentiallyinviscid material 1 under positive pressure supplied to anextrusionorifice 2 in a crucible 3. The molten essentially inviscidfilamentary stream or jet 4 issues from orifice 2 in orifice plate andpasses through inert gas zone or gap 5 formed by the parallelarrangement of the gas plate 6 with the orifice plate 10. Inert gas maybe passed into zone 5 through port 7 shown in pedestal II. The inert gasthen flows through a passage provided by the gas plate throat 8,essentially coaxially aligned with orifice 2, into a second zonecontaining a film-stabilizing atmosphere contained in chamber 9.

Generally, the formation of fibers and filaments by the film stabilizedinviscid spinning process is applicable to the extrusion of jets havingdiameters of less than about 50 mils. It appears that above about 50mils sufficient transfer of heat out of the molten stream, even thoughfilm-stabilized, is difficult to accomplish as a practical matter toprevent breakup even when the jet is extruded into a cooled chamber.Moreover, where large diameter jets are extruded it appears that themomentum of the stream is sut'ficient to remove tubes and other orificeobstructions above-noted. On the other hand, when using the filmstabilization technique fine diameter fibers can adequately cool priorto breakup at room temperature or greater so that there is no necessityfor elaborate cooling systems for chilling or attempting to supercoolthe molten jet. In order to provide sufficient jet lengths initially toprovide for film stabilization of the molten filamentary shaped jet thevelocity of extrusion in a given case should be such that the Rayleighparameter, (Ra), a dimensionless quantity,

lies between 1.5 and 25, where Vis the jet velocity (cm./sec.), D is thejet diameter upon issue (cm.), p and 'y the melt density (gm/cm?) andsurface tension (dynes/cmF), respectively, of

the molten material. Where the velocity is such that the Rayleighparameter falls below about l.5 the jet length may be so short that itnormally cannot be adequately stabilized prior to breakup. Conversely,where the velocity of the molten jet is too high breakup can be causedby aerodynamic deceleration.

As earlier indicated according to this invention the molten essentiallyinviscid jet is extruded directly into a flowing inert gaseousatmosphere which is supplied to the zone between the orifice plate andthe gas plate through the passage provided by the gas plate orifice orthroat and into the film-stabilizing atmosphere where a stabilizing filmis formed and the molten stream is solidified by cooling prior tobreakup. The nature of the inert gas does not appear to be critical aslong as the gas in inert to the extruded materials, the orifice plateand other parts of the extrusion apparatus. Helium and argon have beensuccessfully employed and they may contain other ingredients which wouldinhibit growths in the inert gas zone without attacking the molten jetor the extrusion apparatus. In dealing with inert gases from commercialsources it is usually necessary to treat the gas to remove minorimpurities, such as oxygen, which, even in quantities as high as onepart per million become quite reactive with the met or parts of theextrusion apparatus at highly elevated temperatures. Thus, the term,inert gas," is intended to connote gases having constituents reactive atextrusion temperatures with the molten jet or apparatus inconcentrations of less than about one part per million.

A principal requirement of this invention is that the inert gas velocityin the gas plate throat lies above a minimum value and that the uppervelocity of the gas be such that it does not cause the unstabilized meltto break up into shot. This velocity can readily be regulated by theamount of gas supplied to the inert gas zone in relation to the diameterof the gas plate throat.

The successful operation of this invention requires that the velocity ofthe gas through the throat of the gas plate be maintained above acertain minimum for any given system to preclude diffusion of thefilm-forming gas into the inert gas zone. As a practical matter the gasflow may be measured by a rotameter placed between the inert gas sourceand gas plate. Thus, the volume flow rate or the quantity per unit timeof inert gas supplied to the gas plate, 0, measured on the rotameter orother suitable device at 25 C. must be at least the value wherein K.,(Kf) is at least 8 and preferably 12, T is the temperature of the gaspassing through the gas plate (K.), X (cm.) is the distance from theextrusion orifice to the second zone, normally the length traversed bythe jet in the gap plus the length of the gas plate throat, A is theminimum cross-sectional area (cm?) of the plate throat, A is the moltenjet cross-sectional area (cm?) passing through the throat and Dx is thediffusivity (cc/sec.) of a film-forming gas through an inert gas in thesystem. While spinning runs of substantial periods without streamdeviation and blockage can be performed where K. is 8,.values of K. ofat least 12 are normally required where continuous spinning runs aredesirable.

The upper limit for the amount of inert gas passed through the plate issimply that amount which causes disruption and formation of powder orshot from the nascent inviscid filamentary stream.

Generally speaking the gas entering the chamber becomes heated as itpasses to a gas distribution ring which may conveniently be coaxial withthe orifice and gas plate throat. The gas may be distributed radially orin a direction normal to the met suchthat there is substantial symmetryof flow. This flow is in large measure self-distributing towardsymmetrical flow. The inert gas flow within the limits described servesto maintain the molten jet in a predetermined path and precludesdiffusion of film-forming gases into the orifice throat. The process ofthis invention can, if desired, be employed to produce discontinuousfibers, i.e., those having a significant aspect ratio, for example anaspect ratio greater than five, as opposed to either shot or continuouslengths. Thus, it has been observed that as the inert gas velocity isincreased beyond the velocities which can result in continuous filamentformation, there is an upper velocity region in a given system whereshort fibers are produced. If the velocity of the gas is increasedbeyond the short fiber-forming region of the extruded produce thenbecomes a fine powder, commonly known as shot.

H68. 2 and 2A illustrate a typical gas plate 6 from vertical crosssection and top elevation, respectively, wherein an inert gas enteringport 7 circulates in gas distribution ring 12, passes across land 13 andout of the gas plate throat 8. Other gas distribution means have beensuccessfully employed and except as hereinafter described in greaterdetail the particular geometry of the gas plate has not been found to bea critical feature of this invention.

It has been observed that velocity profiles which apparently developfrom shear forces on the jet within the extrusion orifice are relaxed bypassage of the molten unstabilized jet,

through the gas plate throat. As earlier mentioned velocity profilerelaxation of film stabilized molten inviscid jets presents aconsiderable barrier to the basic nature of film stabilization ofinviscid jets insofar as velocity profile relaxation can effectivelydestroy stabilizing influence of the film. Although velocity profilescan be reduced from parabolic flow by resort to short bore or knife-edgeorifice configurations, the use of such configurations, in turn, causesproblems, particularly in the use of fine diameter orifices attemperatures around 1,000 Ciand greater, because the pressures necessaryto extrude the melt from such orifices place unusually high mechanicalstresses on the thin portion of the orifice plate. Moreover, severeerosion and limited orifice life, even in the strongest materials,renders the use of short bore or knife edge orifices uneconomic as apractical matter. According to the instant invention relaxation ofvelocity profiles can be induced after extrusion of the nascent jet andprior to film stabilization to thereby accommodate the use of long boreorifices (i.e., those having an aspect ratio of greater than about 4),thereby, in turn, making provision for strong orifice plates andreducing the material requirements for high temperature extrusion. Theflow gas through the gas plate within the limitations of this inventioncan be regulated for any given orifice and extruded material toaccommodate velocity profile relaxation prior to film stabilization.

While the invention as above-described can be successfully employed tocorrect stream deviations and relax velocity profiles prior to filmstabilization, the process of this invention may, additionally andadvantageously, be employed to attenuate the nascent jet prior to filmstabilization. The term, attenuation," as herein employed means areduction in the diameter of the met. Reduction in diameter, in turn,results in a higher attenuated jet velocity. in the synthetic fiber andglass fiber arts attenuation is classically achieved by stretching thefilamentary mass while in a highly viscous condition. However, whenmetals and other essentially inviscid inorganic melts are extruded froman orifice in molten filamentary form there is a comparatively sharpzone of solidification. Any attempt to substantially stretch thefilament at or below the zone of solidification results in completedisruption of the fragile liquidous part of the stream. It has now beendiscovered that through the use of the method and apparatus hereindescribed essentially inviscid jets can be attenuated without theapplication of substantial extraneous downstream pull. Thus, accordingto the instant invention an inviscid jet may be attenuated by extrusionof the melt directly into an inert gas and then into a film-formingatmosphere under conditions which establish a pressure gradient betweenthe extrusion orifice and the area principally occupied by thefilm-forming atmosphere. Thus, attenuation is achieved where thepressure in the inert gas zone is less than the pressure exerted on themelt in the orifice and greater than the pressure in the film-formingzone beneath the inert gas plate. The degree of attenuation may bevaried by variations in the pressure gradient; the pressure gradient inturn being varied by the velocity and density of the inert gas in theinert gas zone having a given geometry as hereinafter more fullydescribed. While the theory of attenuation of inviscid jets by the meansherein described is not fully understood, it has been found as apractical matter that attenuation results where there exists such apressure gradient. The pressure gradient may be determined by simplyplacing a pressure gauge on the extrusion orifice in a blank run or byconverting reduced mass flow resulting from back pressure in pressureunits. The degree of attenuation can be ascertained by comparison of aproduct extruded from a given orifice diameter under normal conditionswith a wire product extruded from an orifice of the same diameterthrough the pressure gradient as above defined. The benefits of thecapability to attenuate the jet in an inviscid spinning or extrusionoperation are many both with respect to economic and technicalconsiderations. Thus, steel wire having a 3 mil diameter can be producedwith attenuation by extrusion from a 6 or 9 mil orifice, for example.Insofar as the pressure required to extrude a unit mass of steel from a3 mil orifice is far greater than that required to extrude the sameamount from a 6 or 9 mil orifice attenuation results in greatly reducedextrusion pressure requirements. Reduced extrusion pressurerequirements, in turn, reduce the high temperature strength requirementsof the orifice plate. Furthermore, an orifice having an aspect ratio offive, for example, would be only 15 mils thick, whereas, a plate havinga 9 mil orifice would 45 mils thick using the same aspect ratio. Thus,for a given rate of production of wire of a given diameter attenua tionbeneficially results in reduced extrusion pressures along with thicker(and therefore stronger) orifice plates thereby reducing the hightemperature strength requirements of orifice plate constructionmaterials. Additionally, it has been found that great savings can berealized through the use of larger orifices because they are muchsimpler to fabricate. Moreover, tolerances in larger orifices aregreater than in smaller orifices.

From the foregoing discussion it will be readily apparent that the useof the gas plate beneficially provides the artisan with a ready meansfor controlling fiber diameter.

The apparatus employed in this invention comprises a first platedefining an extrusion orifice and a second plate defining a secondorifice coaxial with said extrusion orifice and having a diameter atleast as large as said extrusion orifice, said first and second platesdefining an enclosed chamber, means for continuously supplying a moltenmaterial first through said extrusion orifice into the chamber and meansfor supplying an inert gas into the chamber.

In a preferred embodiment the apparatus employed in this inventioncomprises a parallel arrangement of a first plate or orifice plate andsecond plate or gas plate defining a first and a second orifice,respectively, each orifice being essentially coaxial with an axis normalto the transverse planes of said first and second plates, said first andsecond plates defining an enclosed chamber, means for supplying anessentially inviscid melt for extrusion through said first orifice intosaid chamber As above-indicated there are practical workingrelationships in the geometry of the apparatus of the instant invention.FIG. 3 is a schematic of a vertical cross section which illustrates therelationship of the orifice plate 10 to the gas plate 6. As earlier setforth the operation of this invention requires concommitant molten jetand inert gas flow through the gas plate throat. Thus, the minimumdiameter of the gas plate throat must at least be large enough for themolten filamentary stream and inert gas to pass through the throat. Thediameter of the gas plate throat is also limited to the diameter atwhich the inert gas can be made to flow through at the required rates.As a practical matter very large diameter plate throats are undesirablebecause the volume of inert gas entering the second zone makes ifdifficult to enable contact between the film stabilizing gas and themolten free stream in the second zone. In order to obtain high gasvelocities through the gas plate throat using reasonable volumes ofinert gas its minimum diameter 15 should lie below thirty times andpreferably below 10 times the extrusion orifice diameter 14.Additionally, the gap 16 in the inert gas zone 5 should be less than 15times the orifice diameter 14 and preferably less than one-half thediameter of the gas plate throat 15. The length of the gas plate throatis normally maintained at less than about 100 times and preferably lessthan 50 times the orifice diameter.

While the drawings and discussions herein relate to certain preferredand simplified gas plate geometries other arrangements may be employed.For example, plate throat 8 may be designed as a truncated cone thetheoretical apex of which may lie either toward or away from theextrusion orifice.

The combination of the gas plate and orifice plate may be assembled in avariety of ways. For example the orifice plate and gas plate may beseparate members inserted in a crucible baseplate. The assembly may beformed by machining the inert gas port, plate gap and plate throat in acrucible baseplate and inserting thereon an insert defining an extrusionorifice. Another variation of the assembly comprises machining the gapin the plate defining the extrusion orifice and fitting a flat platethereunder defining a gas plate throat. Other variations are possibleand will bereadily apparent to those skilled in the art. The materialsfrom which the orifice plate and the gas plate are constructed should beessentially inert, each to the other, under the conditions of theextrusion process. They may, of course, by made from the same material.Moreover, the materials should be selected such that they are, desirablyinert to the molten material and so far as is practical, resistant tothermal shock and possess the mechanical strength to withstand thestresses to which they are put. For example, in the extrusion of metalssuch as copper and ferrous alloys, ceramics such as high densityalumina, magnesia, thoria, beryllia and zirconia are useful materialsfor construction of the apparatus herein described. For high temperatureextrusion processes using ceramic charges materials such as molybdenumand. graphite can be employed. For extrusion processes involving lowertemperatures, stainless steel assemblies have been found to performwell. Other materials and combination of materials may be employedwithin the practice of the instant invention.

The invention is particularly applicable to melt extrusion of lowviscosity inorganic materials by film stabilization such as describedhereinbefore which and includes the extrusion of a variety of metals andtheir alloys such as lead, tin, copper, aluminum, iron and alloysthereof, including stainless steels, carbon steels and others.Additionally the process is also applicable to the extrusion of avariety of ceramic compositions and metalloids which are essentiallyinviscid in the molten phase and which cannot be extruded byconventional polymer and glass extrusion techniques.

The following examples are provided to illustrate results achievedthrough the use of the process of the invention and are not intended tolimit the invention.

EXAMPLE 1 A melt spinning apparatus comprising a crucible having anextrusion orifice and a gas plate situated therebeneath and having a gasplate throat coaxial with the extrusion orifice was employed to spin alead/tin alloy. The extrusion orifice was a straight bore orifice 4 milsin diameter and 4 mils long. The gas plate provided a gap of 7 milsbeneath the lower extremity of the extrusion orifice. The gas platethroat was 13 mils in diameter and 7 mils in length.

The molten lead/tin alloy (62/38 weight at 300 C. was forced through theextrusion orifice by a 20 p.s.i.g. head pressure directly into the gapbetween the orifice and the gas plate occupied by flowing helium gas andthen concurrently with helium through the plate throat and then intoair. The flow rate of helium was measured at 250 cc./min. and althoughthe gas was not preheated its temperature rose to C. through contactwith the molten stream and elements of the assembly. The molten jetremained continuous and did not deviate from a straight path overextended periods of continuous spinning. With 7 other conditionsremaining the same the stream underwent severe deviation resulting inrepeated fiber discontinuities shortly after the helium flow rate wasreduced. Visual examination of the orifice after shutdown revealedmacrogrowths formation at the exit of the extrusion orifice indicatingthat the reduced helium flow had not prevented growths on the orifice.

EXAMPLE ll Example I was repeated except that the temperature of themolten alloy in the crucible was increased to 430 C., and the diameterof the plate throat was increased to 18 mils. Continuous, undeviatedstreaming of the molten jet was achieved at a helium flow rate of 630cc./min. and above.

EXAMPLE [I] Example I was repeated using an extrusion orifice having adiameter of 4 mils and an aspect ratio of 6. The gas plate throat had adiameter of 15 mils, a throat length of 20 mils and a gap between theextrusion orifice and the plate of 15 mils. Helium flow rates wereincrementally increased as indicated in Table l and resulted incorresponding increased jet attenuatron.

Neither discontinuities, stream deviations nor orifice growths werenoted to result from the experiments above noted when steady flow ratesat the indicated levels were maintained.

EXAMPLE lV Under a pressure of 40 p.s.i.g. molten commercial grade 2024aluminum heated to 730 C. was extruded as a free molten stream from a 4mil diameter orifice having an aspect ratio of 6 into flowing helium andthen into air. The gap between the gas plate and the extrusion orificewas 10 mils. The plate throat had a diameter of 18 mils and a length of20 mils. Helium flow rates of 600 cc./min. resulted in uninterruptedcontinuous jets streaming for more than 6 hours. Reduced helium flowrates resulted in the formation of growths at the exit of the extrusionorifice after relatively short streaming periods.

EXAMPLE V EXAMPLE V1 Commercial grade 2024 aluminum alloy was spun as acontinuous filament from a melt at 720 C. into flowing helium and theninto air. The extrusion orifice was 8 mils in diameter .and 48 mils inlength. The plate defining the gas zone was situated 7.5 mils beneaththe orifice and provided an orifice 18 mils in diameter and 22.5 mils inlength, coaxially aligned with the extrusion orifice. Table 11 reflectsvarying degrees of attenuation of the molten free stream prior tosolidification principally as a function of varying helium flow rates.

in the experiments reported in Table 11 there existed a back pressure atthe extrusion orifice caused by the high velocity flow of helium throughthe inert gas zone. The existence of the back pressure at the extrusionorifice results in corresponding reduction in the effective overheadextrusion pressure.

EXAMPLE V11 Commercial grade 2024 aluminum was spun as a molten freestream from an 8 mil diameter orifice (aspect ratio of 4) into an inertgas zone defined by the orifice plate and a gas plate, through the gasplate throat and into air. The gas plate was 7.5 mils beneath theorifice plate. The throat was 25 mils in diameter and 22.5 mils inlength. Several runs were conducted employing extrusion pressures andhelium flow rates indicated in Table 111.

TABLE 111 Extrusion He Flow Fiber Diameter Diameter Pressure Rate(cc/min.) (mils) Reduction(%) (p.s.i.g.)

9 3390 4.9s 33.0 1 3190 est 39.5

EXAMPLE V111 Using an orifice having a 4 mil diameter and an aspectratio of 8 in combination with a gas plate having a throat diameter of18 mils and a throat length of 22.5 mils to provide a gap of 7.5 mils,molten 2024 aluminum at 720 C. was extruded as a free stream directlyinto flowing helium, through the gas plate throat and into air under theconditions indicated in Table IV.

TABLE [V Extrusion He Flow Fiber Diameter Diameter Pressure Rate(cc.lmin.) (mils) Reduction (P- -B-) In the several experiments noted inExample Vll and VIII growths were not observed to form at or within theorifice even after extended periods of extrusion. in each case thereexisted a back pressure at the orifice (observed by slightly diminishedmass flow through the orifice) resulting in attenuation of the moltenfree stream prior to solidification.

Although relaxation of velocity profiles caused by spinning through anorifice having an aspect ration of 8 normally results in disruption ofthe stabilizing film which, in turn, results either in stream disruptionor fibers having spaced modules, smooth fibers were produced in the runsreported in Example V111 indicating that the flow of helium along withthe molten stream through the gas plate throat induces relaxation ofvelocity profiles prior to stabilization.

We claim:

1. An improved orifice assembly for the formation of fibers andfilaments from an essentially inviscid melt by extrusion thereof throughan orifice in an extrusion orifice plate as a free molten filamentarystream in a film-forming atmosphere whereby the stream is maintained infilamentary form by a film until solidified, the improvement comprisinga. a second plate positioned beneath said orifice plate and having anorifice substantially coaxial with said extrusion orifice, said orificeplate and second plate defining an enclosed chamber having a gapdistance therebetween in the vicinity of said orifices less thanone-half the diameter of said second plate orifice, said second plateorifice further having a length less than times the diameter of saidextrusion plate orifice and a diameter less than 30 times the diameterof said extrusion plate orifice; and

b. port means communicating with said enclosed chamber for providing apredetermined flow of inert gas from said port means into said secondplate orifice thereby providing a blanket of inert gas about the moltenstream as it passes through said enclosed chamber and said second plateorifice into the film forming atmosphere.

2. The assembly of claim 1 wherein the diameter of said second orificeis less than 10 times the diameter of said first orifice.

3. The assembly of claim 1 wherein the length of said second orifice isless than 50 times the diameter of said first orifice.

1. An improved orifice assembly for the formation of fibers andfilaments from an essentially inviscid melt by extrusion thereof throughan orifice in an extrusion orifice plate as a free molten filamentarystream in a film-forming atmosphere whereby the stream is maintained infilamentary form by a film until solidified, the improvement comprisinga. a second plate positioned beneath said orifice plate and having anorifice substantially coaxial with said extrusion orifice, said orificeplate and second plate defining an enclosed chamber having a gapdistance therebetween in the vicinity of said orifices less thanone-half the diameter of said second plate orifice, said second plateorifice further having a length less than 100 times the diameter of saidextrusion plate orifice and a diameter less than 30 times the diameterof said extrusion plate orifice; and b. port means communicating withsaid enclosed chamber for providing a predetermined flow of inert gasfrom said port means into said second plate orifice thereby providing ablanket of inert gas about the molten stream as it passes through saidenclosed chamber and said second plate orifice into the film formingatmosphere.
 2. The assembly of claim 1 wherein the diameter of saidsecond orifice is less than 10 times the diameter of said first orifice.3. The assembly of claim 1 wherein the length of said second orifice isless than 50 times the diameter of said first orifice.